What is the lexical environment?

Lexical: "Relating to the words or vocabulary of a language" - Oxford English Dictionary

In programming, this means where a chunk of code physically sits will affect how it is interpreted and executed. In plain terms, a lexical environment is where the code appears and what surrounds it.

Each time you create a new function, this creates another lexical environment:

index.js
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constouter=()=>{
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//thereisalexicalenvironmenthere
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constinner=()=>{
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//thereisanewlexicalenvironmenthere
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}
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}
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//codeonline2willbeinterpreteddifferentlytocodeonline4becausetheyareindifferentlexicalenvironments
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This means there are can be potentially dozens or hundreds of lexical environments within one file.